1. Field of the Invention
The present invention is directed to a process for the preparation of derivatives of halo-but-2-enoic acids and esters high in 2-ene content and their use as catalyst promoters in ethylene polymerization and copolymerization, e.g., the preparation of a-olefin copolymers in which ethylene, at least one other higher a-olefin monomer, and, optionally, a non-conjugated diene, are copolymerized.
2. Description of Related Art
Polymerization of .alpha.-olefins to produce .alpha.-olefin copolymers and EPDM is well established in the art. In these polymerizations, a transition metal catalyst, most often a vanadium catalyst, and an organo-aluminum co-catalyst are added to a reaction mixture to catalyze the polymerization reaction. In order to enhance catalyst efficiency and/or regulate polymer molecular weight, a catalyst activator or promoter is frequently employed, providing the advantages of improved catalyst selectivity and efficiency including diene incorporation.
U.S. Pat. No. 2,515,306 discloses that if the hydrogenation of esters of 2,.omega.,.omega.,.omega.-tetrahalogenoalkanoic acid is carried out in neutral or acid media, i.e., while maintaining the reaction mixture at a pH of not over 7, the 2-halogen atom, i.e., the halogen on the carbon atom adjacent to the carboxyl group, is selectively removed without affecting the halogen atoms of the trihalogenomethyl group. By this method, compounds can be prepared that are useful in numerous syntheses involving reactions, such as, hydrolysis, hydrogenative coupling, dehydrohalogenation, and metathetical replacement.
U.S. Pat. No. 3,743,669 discloses that acrylates, acrylonitrile, acrylamides or vinyl ketones can be reacted, even at ambient temperature, with an aldehyde in the presence of an organic tertiary amine catalyst to produce the corresponding 2-(1-hydroxyalkyl)-acrylates, acrylonitriles, acrylamides or vinyl ketones in very good yields. These product monomers having an --OH moiety in their structure are said to exhibit, upon polymerization, good adhesive properties.
U.S. Pat. No. 5,527,951 discloses that tert-alkylmethoxy-substituted vanadium compounds are useful as catalysts for the polymerization of ethylene or the copolymerization of ethylene with a-olefins and (optionally) nonconjugated polyenes. It is preferred that the catalytic vanadium compound be used in combination with a promoter of a given structure, preferably one selected from the group consisting of butyl 4,4,4-trichlorobut-2-enoate, methyl 2-methyl-4,4,4-trichlorobut-2-enoate, ethyl 4,4,4-trichlorobut-2-enoate, 2-ethylhexyl 4,4,4-trichlorobut-2-enoate, and butyl perchlorocrotonate.
Hoffmann et al., Angew. Chem. Int. Ed. Engl. 22(10):795 (1983) reported that acrylate esters can be coupled readily at the a-position with a wide variety of aldehydes, also sensitive and functionalized representatives, in the presence of catalytic amounts of DABCO (1,4-diaza-bicyclo[2.2.2]octane) at room temperature.
Rabe et al., Angew. Chem. Int. Ed. Engl. 22(10):796-7 (1983) describe a reaction sequence that starts from inexpensive aldehydes and acrylic ester, and stereoselectively affords trisubstituted olefins.
Hill et al., Tetrahedron Letters 27 (41):5007-5010 (1986) disclose that aldehydes and ketones will add to acrylonitrile, acrylate esters, acrolein and .alpha.,.beta.-enones with the formation of a range of 2(X)-propen-1-ols (X=CN, COOR, COR). The reactions are catalyzed by tertiary amines and are very sensitive to pressure. A wide variety of products may be obtained at pressures of 5 kbar or less, whereas most of the reactions do not occur at atmospheric pressure.
Benincasa et al., Tetrahedron Letters 36 (7):1103-1106 (1995) disclose that dimethyl 2,3-dialkyl-2,3-dichloro-butanedioates are efficiently prepared in dimethylformamide or dimethylsulfoxide, through reductive homo-coupling of methyl 2-to bromo-2-chlorocarboxylates promoted by CuBr--Fe.
Brown et al., Organic Syntheses 68:64 (1989) reported that homogeneous hydrogenation of the aldehyde-acrylate condensation products in the presence of organometallic catalysts give predominantly anti-isomers. The catalysts employed here are transitional-metal complexes consisting of complicated coordinating ligands. They also reported in J. Chem. Soc. Chem. Comm. 277-278 (1998) that such diastereoselectivity with these catalysts is observed when the a-hydroxy functional groups of the condensation products are silylated.
The foregoing are incorporated herein by reference in their entirety.